1. Field of the Invention
The present invention relates generally to printing presses and more particularly to a printing press for operating with reduced vibrations.
2. Background Information
Print unit towers have significant side frame vibration while starting up and during operation. One of the major causes of side frame vibration are vibrator rolls, which move laterally so as to provide a more consistent ink coating or dampening solution to a plate cylinder. The vibrations caused by the vibrator rolls may reduce the life of the equipment and also may cause a lateral print double on the printed material, leading to poor print quality and, often, paper waste.
Prior attempts to reduce vibrator roll vibration effects include using a separate motor to drive the lateral motion of the vibrator rolls so that the torque disturbances due to vibrator oscillation can be insulated from the unit drive, or to drive the lateral motion so that vibrator phases can be adjusted relative to one another.
However, using separate motors to drive the vibrator rolls to produce the lateral motion incurs significant additional cost and complexity over the traditional technique of having the lateral and rotational motion of the vibrator rolls driven by the same drive which drives the printing cylinders.
When the lateral motion is driven by the same drive as a corresponding print cylinder, the phasing of the various vibrator rolls for different plate cylinders typically are not controlled, especially if independent motors drive the various plate cylinders. If, for example, during a circumferential registration adjustment of one plate cylinder, the phase of the various vibrator rolls changes, those vibrator rolls may cause increased vibrations, leading to the defects mentioned above.
Japanese Patent Document No. 8-276562 purports to disclose a dynamic dampener for reducing vibrations caused by a reciprocating roller. The dynamic dampener requires a separate device, which can be expensive and can be difficult to maintain.
U.K. Patent Application No. 2 180 502 purports to disclose a device for adjusting the amplitude of the axial reciprocation of ink vibrator rollers. No change in the phasing of the axial reciprocation appears to occur, and the purpose of the device does not appear to be to reduce vibrations in a printing press, but rather to vary the stroke length of the vibrator rollers.
An object of the present invention is to provide a method and device for reducing printing press vibrations in an efficient or cost-effective manner.
The present invention provides a method for reducing vibrations in a printing press having a first plate cylinder independently registrable from a second print cylinder. The first plate cylinder is operatively connected to at least one first laterally-moving vibrator roll and the second plate cylinder is operatively connected to at least one second laterally-moving vibrator roll. The method includes the steps of determining a lateral position of the first vibrator roll with respect to the second vibrator roll, and rotating the first plate cylinder with respect to the second plate cylinder so as to change the lateral position of the first vibrator roll with respect to the second vibrator roll.
By changing the lateral position of the first vibrator roll with respect to the second vibrator roll, and thus the phase between the vibrator rolls, a desired phase difference between the rolls corresponding to operation of the printing press at reduced vibrations can be achieved.
The rotating step preferably includes rotating either the first or second plate cylinder in a single rotation of 360 degrees, or a plurality of single rotations of 360 degrees.
Preferably, a desired phase difference between the first and second vibrator rolls is determined, with the rotating step including rotating the first or second plate cylinder a number of rotations to achieve the desired phase difference.
A lateral position of the first vibrator roll may be fed back to a controller, the controller then controlling the rotating step.
The desired phase difference may be determined using a mathematical model, or by measuring actual vibrations in the press.
If the first and second rolls are at a same height, the first vibrator roll preferably is phased, based on the mathematical model, at 180 degrees from the second vibrator roll after the rotating step.
The present invention also provides a method for reducing vibrations in the printing press comprising the steps of determining a desired lateral position of the first vibrator roll with respect to the second vibrator roll as a function of actual or predicted vibration of the printing press, and rotating the first plate cylinder with respect to the second plate cylinder so as to change the lateral position of the first vibrator roll with respect to the second vibrator roll to the desired lateral position.
Also provided by the present invention is a printing press including a first plate cylinder with at least one first vibrator roll operatively connected to the first plate cylinder. The first vibrator roll is part of an inking unit or a dampening unit, and the first vibrator roll moves laterally a certain amount for each rotation of the first plate cylinder. The press also includes a second plate cylinder independently registrable with respect to the first plate cylinder in a circumferential direction, with at least one second vibrator roll operatively connected to the second plate cylinder. The second vibrator roll is part of another inking unit or another dampening unit, with the second vibrator roll moving laterally a certain amount for each rotation of the second plate cylinder. At least one sensor senses a lateral position of the first vibrator roll with respect to the second vibrator roll or a vibration of the printing press, and a controller receives an input from the at least one sensor. The controller then rotates the first plate cylinder with respect to the second plate cylinder so as to alter a phase between the first vibrator roll and the second vibrator roll as a function of the input.
Preferably the printing press is a lithographic offset printing press having a first blanket cylinder connected to the first plate cylinder and a second blanket cylinder connected to the second plate cylinder.
A first motor preferably drives the first plate cylinder and the first vibrator roll and a second motor drives the second plate cylinder and the second vibrator roll.
At least two first vibrator rolls and at least two second vibrator rolls preferably are present, with at least one being for the inking unit and at least one for the dampening unit.
The sensor may include a first sensor to monitor a first vibrator roll lateral position and a second sensor to monitor a second vibrator roll lateral position.
The sensor may be an accelerometer or other device measuring the vibration of the press.